A roll bearing for a continuous hot dipping bath has generally been fashioned of a stainless steel, high-chromium steel, sintered carbide, etc. representing materials having excellent properties with respect to corrosion resistance, through build-up welding or a sleeve type construction. However, these materials wear and can be damaged, for example, after about one week of immersion in a hot zinc dipping bath. As a result of the damage, a play results between a roll shaft and the roll bearing, and a roll and a hot dipping apparatus will oscillate, thereby adversely affecting the plating property. It has been found that it is difficult to completely prevent corrosion of a metal due to molten metal even if the metal, relatively excellent with respect to corrosion resistance, such as, for example, stainless steel, high-chromium steel and sintered carbide is employed. Consequently, corrosion wear due to molten metal as well as friction is caused at the time of sliding of the roll bearing, thus increasing the wearing depth. It has also been determined that when corrosion reaches a certain stage, corrosion pits are formed in the sliding surfaces of the roll shaft and bearing thereby promoting additional wear due to friction.
In order to decrease the wearing of the roll bearing, it is necessary to select a material which is excellent in corrosion resistance against molten metal. In this connection, some ceramics exhibit little corrosion due to molten metal, and such ceramics can be regarded as the optimum material for a roll bearing for a hot dipping bath.
In, for example, JP-A-3-177552, a bearing for a continuously operating hot dipping bath is proposed wherein a sintered ceramic member is closely fitted on the outer peripheral surface of a roll shaft through a metallic buffer material, and a solid lubricant ceramic material is provided on an inner peripheral surface of the bearing.
In the above-described conventional technique, problems of a combination of the ceramic and the solid lubricant during actual operation in the continuous hot dipping bath are not considered.
In other words, it has been determined that although ceramics are excellent in corrosion resistance against molten metal, a new problem arises, namely that of inter metallic compounds generated as a result of a reaction between various metallic construction members in a hot dipping bath tank and the molten metal adversely affecting the solid lubricant.